1. Field of the Invention
The present invention relates to a nonreducible dielectric composition to be applied to a laminated ceramic capacitor for temperature compensation, and the like, and more particularly, to a nonreducible dielectric composition having a high insulation resistance and a small dielectric loss, which can be sintered under a reducing atmosphere using an internal electrode containing nickel (Ni).
2. Description of the Related Art
Demand for laminated ceramic capacitors is increasing yearly due to digitalization, miniaturization and high-functionalization of electronic products, and they have been used in a variety of electronic devices such as televisions, computers, video cameras, cellular phones and the like. In recent years, there has been an increased need for a laminated ceramic capacitor having excellent characteristics, that is, a high insulation resistance, a small dielectric loss, and a reduced variation in capacitance upon a variation in temperature.
A conventional laminated ceramic capacitor was manufactured by sintering a high-priced noble metal such as palladium (Pd) or silver-palladium (Ag—Pd) alloy including palladium as an internal electrode, and a BaO—Nd2O3—TiO2— or MgTiO3—CaTiO3—based dielectric composition under an atmosphere of 1,100-1,350° C. However, there have been problems in that due to oxygen vacancies formed when sintered under a reducing atmosphere, the composition exhibits a lowered insulation resistance and a degraded reliability, and thus Ni cannot be employed as an internal electrode.
In order to use nickel as an internal electrode, such a composition must be able to be sintered under a reducing atmosphere. Known up until now has been a CSZT based composition disclosed in Japanese Patent Laid-Open Publication No. 10-335169. The composition consists of a main component expressed by the general formula, (Ca1-xSrx)m(Zr1-yTiy)O3, which meets the conditions: 0≦x≦1, 0≦y≦0.1 and 0.75≦m≦1.04; and a minor component of BCG: 0.5-15 mol %, MnO: 0.2-5 mol %, Al2O3: 0.1-10 mol % (on the basis of the total moles of the main component) and a rare earth element.
The composition disclosed in the above publication has advantages of nonreducibiliy and a reduced variation in capacitance upon a variation in temperature. Furthermore, the composition overcomes a large dielectric loss at high temperature-low frequency condition encountered in lithium glass (Li-glass) based composition. Also, the composition is characterized in that uniform and small grain size can be obtained.
In spite of these advantages, in the above composition, the sintering temperature of dielectric is as high as 1,300° C., and the sintering initiating temperature of dielectric is higher than that of Ni used for an internal electrode. As a result, there is a problem in that cracks, defects or the like are caused by mismatching between the internal electrode and ceramic. This is because the metal of the electrode exhibits a shrinkage rate higher than that of ceramic during the sintering process.
Meanwhile, Japanese Patent Laid-Open Publication No. 63-289709 discloses a composition consisting of a main component, (CaxSr1-x)m(ZryTi1-y)O3 (0.3≦x≦0.5, 0.92≦y≦0.98, and 0.95≦m≦1.08) and a minor component, MnO2(0.01-4.0 wt %) and SiO2(2.0-8.0 wt %), the composition being sinterable under a reducing atmosphere. The dielectric constant of Ca/Sr in the composition is relatively high, below 1.
Nevertheless, the above composition still has a problem in that a dielectric loss at high temperature—low frequency condition is large. Furthermore, the composition involves generation of defects by mismatching between electrode metal and ceramic during a sintering process, because sintering temperature of ceramic is high, up to 1,300° C.